California's health exchange said it would use an additional $155 million in federal grant money to address customer service woes and to boost low enrollment among the key market of uninsured Latinos.

The Covered California exchange announced the injection of money from the Obama administration Thursday as it faced growing criticism for dismal service and a disappointing sign-up rate among Latinos.

The state has led the nation with more than 625,000 people enrolled in health plans through mid-January, and it's a bellwether state for the national rollout of the Affordable Care Act.

That large volume of enrollment, much of it coming last month, has often overwhelmed the state exchange and its participating health plans. Consumers, insurance agents and enrollment counselors have complained about extremely long wait times on the phone and about website glitches that have slowed the application process and caused considerable confusion.

Covered California said Thursday that 51% of callers in December couldn't get through and abandoned their call. The state's goal was that fewer than 3% of calls would be abandoned. In addition, 53% of callers got a busy signal and fewer than 1% of calls were answered within 30 seconds.

Exchange officials acknowledged the state's performance has been unacceptable at times. "We have not provided good customer service," said Peter Lee, executive director of Covered California.

To address those problems, Covered California said, it will use some of the new federal funding to hire 350 more service-center workers before open enrollment ends March 31. The state said it had 469 call-center representatives Jan. 1.

The exchange said it also plans to spend nearly $10 million more on marketing aimed at Latinos and young people, another key market in the healthcare law rollout, to balance out older, sicker enrollees.

About 1.2 million people, or 46%, of the 2.6 million Californians eligible for federal premium subsidies are Latino. But Covered California said this week that only 20% of enrollees through the end of December described themselves as Latino.

At the exchange's Thursday board meeting, a state lawmaker and many patient advocates questioned the need for more advertising geared to Latinos and said improving customer service should be the priority.

Paul Fearer, a Covered California board member, said he shared those concerns about seeking out more applicants if the exchange can't meet their needs.

"If we spend millions on marketing and in fact our customer service isn't up to it, we may actually do more harm than good," Fearer said. "I'm concerned about ramping up media if we aren't fully prepared and ready to give excellent customer service."

Lee defended the increased marketing as a way to inform people about how to get in-person help in their community. Critics have cited a shortage of local enrollment counselors, particularly to assist Spanish-speaking consumers.

Covered California has 3,729 enrollment counselors and 60% of them speak Spanish, according to the state.

The latest funding of $155 million comes atop the $910 million in federal grant money Covered California has received to establish the state exchange.